Stepping motor

ABSTRACT

A stepping motor is disclosed for use in imparting to a rotatable member an intermittent step-by-step rotating motion by means of a linearly reciprocating driving member. The driven, rotatable member has a shaft which carries a ratchet wheel and is advanced intermittently by two oppositely positioned pawls, mounted on a reciprocating driving member so that both movements of the driver will rotate the driven member another step. Means are also provided for preventing undesirable rotation of the ratchet, not only in the drive direction thereof, but also in the reverse direction, and may include a stop block cooperating with each pawl or a second ratchet wheel cooperating with other stop members. Furthermore, novel means for reciprocating the driver which may include electrical, pneumatic or mechanical means or a combination thereof is also disclosed.

United States Patent [191 Scholin 1 Mar. 4, 1975 STEPPING MOTOR [75]Inventor: Harold W. Scholin, Park Ridge, 111.

[73] Assignee: Scholin Industries, llnc., Chicago, Ill.

[22] Filed: Jan. 14, 1974 [21 App]. No: 433,102

Primary E.raminer-Samuel Scott Assistant Examiner-F. D. ShoemakerAttorney, Agent, or Firm-Root & OKeeffe 57 ABSTRACT A stepping motor isdisclosed for use in imparting to a rotatable member an intermittentstep-by-step rotating motion by means of a linearly reciprocatingdriving member. The driven, rotatable member has a shaft which carries aratchet wheel and is advanced intermittently by two oppositelypositioned pawls. mounted on a reciprocating driving member so that bothmove ments of the driver will rotate the driven member another step.Means are also provided for preventing undesirable rotation of theratchet, not only in the drive direction thereof, but also in thereverse direction, and may include a stop block cooperating with eachpawl,

or a second ratchet wheel cooperating with other stop members.Furthermore, novel means for reciprocating the driver which may includeelectrical, pneumatic or mechanical means or a combination thereof isalso disclosed.

24 Claims, 12 Drawing Figures PATENTED MAR 4 5 SHEET 3 0F 6 PATENTEUHAR4W5 I sum 5 er a q368,861

STEPPING MOTOR BACKGROUND OF THE INVENTION Stepping motors have beenknown heretofore, wherein a reciprocating pawl engages a ratchet wheelto advance a rotary member intermittently which is coupled thereto.Also, means have been provided in the past to restrain the rotation ofthe ratchet wheel in both the drive and reverse directions, such as, forexample, as disclosed in the Fredell US. Pat. No. 3,501,968, issued Mar.24, 1970. Such devices, however, have limitations, such as the speed orfrequency of the stepping action. The present device involves a noveldesign which enables the frequency of the stepping action to beincreased by at least double that which was previously known.

When the frequency of stepping is thus increased, however, otherproblems arise in connection with the means for restraining movement ofthe wheel in both directions and novel means have been provided hereinto effectively restrain unwanted movement of the ratchet wheel, even atvery high speeds.

BRIEF SUMMARY OF THE INVENTION The invention is directed to a novelstepping motor for rapidly rotating, intermittently, a shaft for theperformance of some additional function. It involves more particularly,the use of a driving member reciprocating a linear path on which ismounted two pawls in opposing relation. A ratchet wheel mounted on thedriven shaft is disposed in operative relation to both pawls so that thewheel and shaft are advanced one step for each direction ofreciprocation of the driving member.

In one form of the invention, a stop block is mounted adjacent each pawlon the supporting frame of the driving member which wedges itsassociated pawl at the end of the driving stroke thereof in such a wayas to lock the ratchet wheel against movement in both directions.

This function may also be accomplished in another form of the inventionby providing two ratchet wheels on the driven shaft having teethdisposed in opposite directions, one of which is driven by the pawls andthe other of which cooperates with stop members mounted on the drivingmember to restrain movement of the driven member in either direction.

A further feature of the invention is the novel means for reciprocatingthe driving member. Although any known means may be used for thispurpose, such as a crank or eccentric, I prefer .to use a combination ofelectrical and pneumatic forces wherein an electrically operated spoolvalveis used to direct air to one or the other of two cylinders whichmoves a piston member, which, in turn, controls the operation of thedriving member.

As may become more apparent, as the description proceeds, in one formofthis latter feature, such piston 472,489 filed May 22, 1974, there maybe conditions wherein the natural frictional forces of the drum may beovercome by other forces associated with the drum and drive the assemblyahead of the indexing pawl. To overcome this, I have provided anadditional feature which includes a deceleration plunger assemblyoperable to control the ratchet assembly and index drum to prevent thedrum from accelerating away from the driving pawl.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of oneform of present invention with the reciprocating driving member in itslower position, but showing the driving means to reciprocate the drivingmember in vertical section.

FIG. 2 is a side elevational view of the assembly, shown in FIG. 1.

FIG. 3 is a view similar to FIG. 1 but illustrating the reciprocatingdriving member in an intermediate positron.

FIG. 4 is a view similar to FIGS. 1 and 3 but showing the driving memberin its uppermost position.

FIG. 5 is a somewhat diagrammatic view of the device of FIG. 1 on asmaller scale, showing a modified form of the means for reciprocatingthe driving member.

FIG. 6 is a view similar to FIG. 1 but showing a still further modifiedform of the means for reciprocating the driving member.

FIG. 7 is an elevational view of the reciprocating driving member in itslowest position, illustrating a modified arrangement of restrainingmeans for preventing unwanted rotation of the driven member in bothdirections.

FIG. 8 is a view similar to FIG. 7 but showing the re ciprocatingdriving member in the uppermost position thereof.

FIG. 9 is a vertical sectional view taken substantially along the planeof line 9--9 of FIG. 7.

FIG. 10 is an elevational view similar to FIG. 7 with parts broken awayand shown in section and illustrating additional means for restrainingunwanted rotation of the driven member in a situation where externalforces tend to overcome the frictional forces of the driven member andmove it an additional amount.

FIG. 11 is a fragmentary vertical sectional view, taken substantiallyalong the plane of line 11-11 of FIG. 10, and

FIG. 12 is a fragmentary, vertical sectional view, taken substantiallyalong the plane of line l212 of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION Referring now, more particularly,to FIGS. 1 through 4, there will be seen a frame, generally indicated bythe numeral 1, which consists of the two side members 2 and 3, a topcrossbar 4, and a bottom crossbar 5. This frame is mounted on asupporting plate 6.

A driving member 7 is mounted within the frame I for reciprocatingsliding movement, as will appear presently. This driving member isprovided with an opening 8 in substantially the center thereof and has alower extension 9, extending downwardly from one side thereof on whichis pivotally mounted the pawl 10 by means of the pivot pin 11. A tensionspring 12 is secured at one end thereof to the driving member 7 by meansof the pin 13 and at the other end thereof to a pin 14 on the pawl. Thisspring, then, normally urges the pawl toward the left, as viewed in thevarious figures.

At the upper part of the driving member, there is provided an upperextension at one side thereof indicated at 15. A second pawl ispivotally mounted on this upper extension by means of the pivot pin 17,and this pawl is normally urged toward the right, as viewed in thevarious figures, by means of a tension spring 18 anchored at one endthereof to the pin 19 on the driving member, and at the other endthereof to a pin 20, mounted on the pawl.

A ratchet wheel 21 has a hub portion 22 thereon which receives the shaft23 and is coupled thereto by means of the key 24. The ratchet wheel 21and the teeth 25 thereon are arranged to be in the same plane with thetwo pawls l and 16, so that, on reciprocation of the driving member 7,the two pawls will drive the ratchet wheel and the shaft 23 to which itis coupled. It is apparent in viewing these various figures that whenthe driving member moves upwardly, the pawl will advance the ratchetwheel one step because the upper end thereof contacts the teeth of thewheel and moves it from the position shown in FIG. 1 through theposition shown in FIG. 3 and to the position thereof shown in FIG. 4.

During this movement, the upper pawl 16 will be carried upwardly withthe driving member from the posi tion shown in FIG. 1 through theposition thereof shown in FIG. 3, and to its position shown in FIG. 4.During downward movement of the driving member, the reverse action takesplace, wherein the upper pawl 16 will move downwardly and will move theratchet wheel and the shaft 23 another step in a counterclockwisedirection, as viewed in the various figures. The opposed sides of thedriving member 7 are received in guideways provided on the innersurfaces of the two side members 2 and 3 of the frame 1. Thus, thedriving member will be guided in its reciprocating movement.

It will be evident that any suitable device can be con nected to theshaft 23 to be driven thereby in a step-bystep fashion. As mentionedhereinabove, the particular device which has been designed for use inconnection with the present invention is more fully disclosed andclaimed in my co-pending application above referred IO.

In any event, it is important in any indexing device of this nature thatmeans be provided to prevent any unwanted motion of the ratchet wheeland shaft, such as by overrunning in the driving direction or rotatingin the reverse direction after completing an indexing step.

One of the means which has been found useful for this purpose includes astop block or wedge member associated with each of the pawls. As shownherein, there is a stop block 26 mounted on the frame for cooperationwith the pawl 10, and another stop block 27 on the opposite side of theframe which cooperates with the pawl 16. The action of each of theseblocks is such that the pawl which is driving the ratchet wheel and theedge of the block, after completion of the indexing stroke. as may beseen in FIG. 4, thereby preventing rotation of the ratchet wheel ineither direction.

As may be seen in FIG. 1, the driving member 7 is in its lowermostposition where the upper pawl 16 has just completed an indexing advanceof the ratchet wheel. In this position of the parts, the upper end ofthe lower pawl 10 is spaced downwardly from the tooth on the wheel whichit will engage to advance the wheel. FIG.

3 shows the driving member after it has moved up wardly a short distanceto the point where the upper end of the pawl 10 just contacts the nexttooth on the wheel. It will be noted here that the outermost end of eachof the pawls l0 and 16 is provided with an inclined 10a and 16a,respectively, which forms an acute angle with the inner side of the pawland an obtuse angle with the outer side of the pawl, thereby forming thecorners 10b and 161; respectively.

The angle of this inclined surface is such that, when a pawl reaches thetooth on the ratchet wheel to begin the next indexing movement, thecorner which forms the obtuse angle on the opposite pawl is at aposition where it just clears the rounded corner of its associated stopblock. For example, in FIG. 3, it will be noted that the pawl 10 hasmoved upwardly to the point where it has just contacted a tooth on theratchet wheel. In this position, the outer corner 16b of the pawl 16 isin a position where it just clears the corner of the stop block 27. Thisis necessary because when the ratchet wheel begins to rotate, the pawlopposite the driving pawl will be urged outwardly and it must be free todo this. For example, if the outer side ofthe pawl is of such lengththat it does not clear the stop block at the moment the driving pawlbegins to rotate the ratchet wheel, then such rotation cannot take placebecause the opposite pawl would still be locked or wedged between theratchel wheel and the stop block. On the other hand,

if such outer side of the pawl is too short, it will not reach the stopblock, as soon as it should when it is driving the ratchet wheel and,therefore, will not become locked to prevent overrunning of the ratchetwheel in the driving direction thereof.

If desired, as an additional precautionary measure, a supplemental stopmember 28 may be pivotally mounted on the frame, at a suitable location,by means of the pivot pin 29. A tension spring 30 urges the outer end 31of such member against the toothed surface of the ratchet, so that, whenthe ratchet is being advanced, the stop member will be cammed out of theway, but as soon as a tooth has passed the end of the member, it willreturn to be positioned in the path of such tooth and prevent rotationof the ratchet in the opposite direction.

The corners of the stop blocks 26 and 27 are rounded, as mentionedabove, and this is an important feature where two pawls are used, asdisclosed herein, and this is where the proper angle of the inclinedends and 16a thereon comes into play, as will presently be seen.

It is possible that, in the use of compressed air, the air pressure maydrop, or may be turned off, or the spool in the control valve mightshift arbitrarily. Any of these things could happen at any point in thecycle. If, for example, the driving member stops or reverses itselfbefore the driving pawl has reached the tooth on the ratchet wheel, thenthere is no problem. On the other hand, if the driving pawl has movedfar enough in the driving direction to begin rotation of the ratchetwheel, but is reversed before the other pawl has reached the next tooth,then the device is out of phase and the face of the ratchet must berepositioned. In this event, the other pawl, which was supposed to beleaving the ratchet wheel, moves in the reverse direction and theinclined surface on the end thereof will cam the pawl on the roundedcorner of the stop block against the ratchet wheel, which will therebyreposition the wheel by rotating it a slight amount in the reversedirection thereof, and the device will not jam.

In the preferred form of the invention, a novel electro-pneumatic drivesystem for reciprocating the driving member 7 is provided. Althoughother drive systems may be used for this purpose, depending upon thetype of member being indexed, and its function, the present system hasbeen found in actual practice to perform rapidly and effectively.

Referring again to FIGS. 1 through 4 of the drawings, the preferredembodiment of this electro-pneumatic drive system includes an aircylinder and piston at each end of the frame having a member movablewith the piston and against the driving member, whereby upward movementof the lower piston will drive the driving member upwardly, and downwardmovement of the upper piston will drive the driving member downwardly.

Electrical control means operable in response to movement of the drivingmember 7 operates an air valve to direct air to one or the other of theair cylinders.

In the drawings, the lower air cylinder is indicated by the numeral 32,and is mounted on the lower cross member 5. It is provided with an airinlet 33 in the bottom thereof, to which may be connected an air conduit(not shown). The other end of such conduit is connected to a source ofair under pressure.

A piston 34, having a sealing ring 35 is snugly received within thecylinder 32 and is reciprocable therein. The piston 34 extends upwardlythrough a suitable opening in the lower cross member 5, and is providedwith an axially extending bore 36. The bottom of the bore 36 ispreferably tapered, as shown at 37 to receive the tapered lower end ofapin 38. The sides of the taper on the lower end of the pin 38 preferablyform a smaller angle than the sides of the taper 37 at the bottom of thebore 36, and the diameter of the pin 38 is less than the diameter of thebore 36, thereby to allow a certain amount of play or freedom ofmovement between the pin and the bore, which results in a floating pm.

The upper end of the pin 38 protrudes beyond the upper end of the piston34, and is received within a recess in the bottom of the driving member7, the inner end of which is tapered. The upper end of the pin 38 islikewise tapered and the sides of the taper form a smaller angle than dothe tapered sides ofthe inner end of the recess 39, thereby to allowfreedom of movement between the pin 38 and said recess.

An upper air cylinder 40 is secured to the upper cross member 4 of theframe, and is provided with a similar piston 41, reciprocable therein.The upper end of the cylinder 40 has an air inlet 42 to which isconnected an air conduit (not shown). The other end of such conduit islikewise connected to the source of compressed air, so that when airunder pressure is directed to the cylinder 40, it will drive the piston41 downwardly.

The piston 41 is likewise provided with an axially extending bore 43,which receives the pin 44, having a smaller diameter than that of thebore. The upper or inner end of the bore 43 is likewise tapered, as at45, to receive the tapered end 46 of the pin 44.

The outer or lower end of the pin 44 is similarly tapered, and isreceived within a recess in the top of the driving member 7, the sidesat the bottom thereof being tapered, as at 47. The tapered ends of thepin 44 have a similar relationship to the tapered bottom of the bore andbottom of the recess to that described above, thereby to allow the pinto float. It will be evident from the foregoing, therefore, that whenair under pressure is admitted to the opening 33 in the bottom ofcylinder 32, the piston 34 thereof will move upwardly carrying with itthe floating pin 38. The upper end of this pin, being received in arecess in the bottom of the driving member 7, will thereupon move thedriving member in an upward direction. Prior to this movement of thedriving member, it had been driven downwardly by the compressed airadmitted through the inlet 42 of the cylinder 40. The valving is suchthat when air is admitted into the cylinder 32, the air pressure in thecylinder 40 above the piston 41 will be relieved through the opening 42,to allow the driving member to move upwardly.

When the driving member has reached its uppermost position and theratchet wheel, together with the shaft on which it is mounted, has beenindexed through one complete step, the cycle will be reversed, byadmitting compressed air to cylinder 40 through the inlet 42 to drivethe driving member downwardly, whereupon the air pressure in thecylinder 32 will be relieved through the opening 33 therein. Thiscycling of the motor and stepping of the ratchet wheel will continueunder normal operation, very rapidly, and the construction is such thatthe reciprocation may take place at a very high speed.

As a matter of fact, it has been found very desirable, although notabsolutely necessary, that some means be provided to buffer the movementof the driving member when it is being driven at relatively high speeds.While any type ofa yieldable member may be provided for this purpose, Ihave shown herein such a high speed buffer arrangement, consisting of apin 48 at one end of the device, around which is located a coiledcompression spring 49, one end of which bears against the upper surfaceof the driving member 7 and the other end of which bears against theunderside of the upper cross member 4.

There is a similar arrangement at the bottom of the driving member,wherein there is: provided a pin 50, around which is located the coiledcompression spring 51, the upper end of which bears against the lowerend of the driving member, and the lower end of which bears against thelower cross member 5. When the motor is being operated at very highspeeds, these springs 49 and 51 will act as buffers and absorb anyshocks due to the rapid reciprocating movement of the driving member.

As mentioned hereinabove, the compressed air is directed, alternately,to the upper and lower cylinders by means of a conventional 4 way spoolvalve (not shown). This valve may be controlled either pneumatically orelectrically, but it has been determined that perhaps the moreeconomical arrangement, and just as practical, is to control this valveelectrically. As also mentioned above, the operation of the valve iscontrolled electrically by the operation of the driving member, itself.

The spool valve to direct air under pressure to the upper and lowercylinders may be of any common and well-known construction and need notbe shown here. Furthermore, the actuation of such a spool valve,electrically, is also known by those skilled in the art. The novelty inthis arrangement, however, resides in the operation of the electricalcircuit to shift the valve in response to movement of the drivingmember. To this end, therefore, there is provided in association withthe upper and lower ends of the driving member, a switch which may becontacted by actuating means on the upper and lower end of the drivingmember.

Referring more particularly to the drawings, it will be noted that belowthe frame member 1, there is mounted a switch 52, provided with anoperating button 53 thereon. When this button is depressed, the spoolvalve of the control will be shifted to direct air under pressure to thecylinder 32 and move the driving member upwardly. This accomplished bymeans of the actuating stud 54, mounted on the lower extension 9 of thedriving member, which extends downwardly through an opening in the lowercross member 5, and may be adjusted to such length that when the drivingmember is moved to its lowermost position, the lower end of the stud 54will contact and depress the actuating button 53 of switch 52, to shiftthe valve.

A similar arrangement is provided at the upper part of the assembly,wherein it will be noted there is a switch 55, having the operatingbutton 56 associated therewith. An upper actuating stud 57 is secured tothe upper extension 15 of the driving member, and passes upwardlythrough the upper cross member 4. The length of this stud may beadjusted so that in the uppermost position of the driving member, itwill depress the button 56, and electrically shift the control spoolvalve to direct air to the upper cylinder 40, thereby to move thedriving member downwardly.

Since the spool constitutes a 4-way valve, its operation is such thatwhen air is directed to the upper cylinder 40, the air pressure in thelower cylinder 32 will be relieved. Likewise, when the driving memberhas reached its lowermost position, the operation of the switchingdevice is such that the spool will be shifted to direct air into thecylinder 32, and will simultaneously relieve the air pressure in theupper cylinder 40.

It will thus become evident upon consideration of the foregoing, that inthis preferred form of the invention, I have provided a novelarrangement of electrical and pneumatic means for reciprocating thedriving member of the stepping motor, and have further provided a novelconnecting means between the pistons of the actuating mechanism and thedriving member, comprising a floating pin, whereby there will be nobinding or jamming of the operating parts, even at extremely highspeeds. Furthermore, the provision of the two oppositely disposed pawlsenables the motor to be operated rapidly, and to index at an extremelyhigh rate of speed. The provision of the stop blocks with the roundedcorners thereon cooperating with each of the pawls which have their endsinclined at a predetermined angle, makes it possible to prevent jammingor out-of-phase positioning of the ratchet wheel, when the air pressureis inadvertently reduced or is turned off.

The other forms of the invention now to be discussed also have theseadvantages. FIG. 5 shows a modified form of the invention wherein aneccentric or crank arrangement is utilized for reciprocating the drivingmember. For example, a motor 58 may be provided with a shaft 59, onwhich is mounted an eccentric 60 to which is connected one end of a link61. The other end ofthis link may extend upwardly through the lowercross member 5 of the frame, and be connected to the driving member suchas by means of the lower extension 9. It will be evident that rotationof the crank 60 will reciprocate the link 61 together with the drivingmember 7 to which it is connected.

-In this form of the invention, the two pawls are still provided,together with the two stop blocks 26 and 27 with their corners rounded,and thus the same advantages heretofore described with respect to FIGS.1 through 4 are present in the construction of FIG. 5. This arrangementmay be suitable for some uses wherein it is not necessary or desirableto reciprocate the driving member at an extremely high rate of speed.

Referring now to FIG. 6, there is illustrated therein a still furthermodified form of a driving means to reciprocate the driving member 7.This alternative form of the invention may also utilize the electricalcircuitry for shifting the spool control valve, and compressed air, asthe driving means. In this instance, however, there is but a singlepiston and cylinder arrangement, wherein air is directed to one end orthe other of a double acting piston.

The cylinder in this form is indicated in FIG. 6 by the numeral 62, andthe usual double acting piston may be disposed therein. An opening forcompressed air below the piston is indicated at 63, and the otheropening, above the piston, for admitting compressed air thereto isindicated by the numeral 64. The piston therein is provided with anupwardly extending piston rod 65, which may be suitably connected to acoupling member 66, secured to the bottom of the driving member 7.

It will thus be evident that when the piston within the cylinder 62 ismoving upwardly, it will drive the member 7 in an upward direction inthe same manner as heretofore described with respect to FIGS. 1 to 4. Inthis instance, however, as soon as the driving member reaches itsuppermost position, the stud 57 will depress the switch button 56 toshift the control spool and relieve the air from below the piston, andadmit air under pressure through the opening 64 into the cylinder abovethe piston, thereupon driving the member 7 in a downward direction.Other than this, the arrangement and operation are the same as orsimilar to that described with respect to FIGS. 1 to 4. In the samemanner, when the driving member reaches its lowermost position, theactuating stud 54 will depress the button 53 to actuate the switch 52and shift the control valve so that it will direct air into the cylinder62 below the piston through the inlet 63, thereby to drive the member 7upwardly.

Referring now to the modified form of the invention shown in FIGS. 7, 8and 9, there is illustrated the same driving member 7 together with thesame pawls l0 and 16 mounted thereon, as well as the electro-pneumaticdriving system incorporating the upper and lower cylinders 41 and 32,respectively, as described hereinabove. It will be noted, however, thatthis particular form of the invention has eliminated stop blocks 26 and27, and has provided instead, an improved type of locking arrangement toprevent inadvertent or unwanted rotation of the ratchet wheel in eitherdirection. Otherwise, the remainder of the structure may be the same asthat disclosed in FIGS. 1 through 4, or in FIG. 5, or in FIG. 6.

In FIGS. 7 through 9, there is provided not only the driving ratchetwheel 21, but also a second ratchet wheel 67, both of which may beformed with a hub 22a keyed to the shaft 23a. The teeth on the secondratchet wheel are disposed in a direction opposite to that in which theteeth 25 on the driving ratchet is directed.

These teeth may be seen in FIGS. 7 and 8, and are indicated by thenumeral 68.

When the driving member is reciprocated so that either one of the pawls10 or 16 contacts a tooth on the ratchet wheel 21 to drive it in acounterclockwise direction, the second ratchet wheel 67 will likewise bedriven in a counterclockwise direction, but the teeth thereon will beoppositely disposed.

The stop members in this form of the invention include a lower block 69and a similar upper block 70, both ofwhich are mounted on the drivingmember 7 for movement therewith. Each of the stop blocks, preferably,has a substantially rectangular configuration with the block 69 havingthe inner edge 71 and the outer edge 72, and with the block 70 having aninner edge 73 and an outer edge 74. The uppermost edge 75 of the lowerblock 69 is preferably inclined, as shown, and the lower edge of theblock 70 is likewise preferably inclined as indicated at 76.

In the lowermost position of the driving member, as shown in FIG. 7, thepawl 16 hasjust driven the ratchet wheel 21 one step in acounterclockwise direction, and it will be noted that in this positionof the various parts, the upper stop block 70 will have been moved intoa position where it is in the path of movement of a tooth 68 on thesecond ratchet wheel 67. Thus, in this position, the ratchet wheel willbe positively stopped against any further movement in the indexing ordriving direction thereof. The ratchet wheel likewise will be preventedfrom any inadvertent rotation in the reverse direction thereof becauseit is locked by the pawl itself.

When the direction of movement ofthe driving memher 7 is reversed, andwhile the pawl 10 is moving up- \vardly to the point where it contactsthe next tooth on the ratchet wheel 21, the stop block 70 will likewisemove upwardly and out of the path of the tooth 68 on the second ratchetwheel 67. Thus, when the ratchet wheels begin to rotate, the stop block70 will be out of the way and the stop block 69 will be moving upwardly.Prior to the time that the indexing step is completed, the stop block 69will have reached a position in the path of movement of the next tooth68 on the second ratchet wheel 67, so that at the end of the indexingstep, such tooth will come against the stop block 69 which will preventany overrunning of the ratchet wheel in the driving direction.

Reference will now be made to FIGS. 10,11, and 12, where the samegeneral arrangement of the driving means and the double ratchet wheelsare shown, as in FIGS. 7, 8 and 9, but, in addition, there isillustrated as deceleration plunger assembly which may be desirableunder some circumstances and the operation of which will appearpresently. This particular improvement has been devised as an additionalsafety measure against overrunning of the ratchet wheel, where thedevice being indexed is such as to have some external forces which maytend to drive the ratchet wheel in the driving direction at such speedand at such force as to overcome the natural frictional forces in theassembly and drive the ratchet ahead of the indexing pawl.

This has been found to occur, on occasion, in the driving of theprogramming drum, which is the subject matter of my above-referred toco-pending application. It has been found, for example, that situationsmay arise where the index drum rotates at a speed greater than thedriving pawl that is driving the drum. The construction is such that thenet effect may be to overcome occur, the teeth on the second ratchetwheel will miss stopping engagement with thestop block on the drivingmember. This deceleration plunger assembly has been designed to overcomethis problem.

In general, the assembly consists of an impact pin, a guide block and astop block. Referring now to FIGS. 10, 11 and 12, the stop block ismounted on the frame 1 and is indicated by the numeral 77. The impactpin 78 is adapted to reciprocate in an axial direction within the guideblock 79. The guide block 79 is provided with an axial bore 80 and ismounted on the supporting plate 6. A coiled compression spring 81. ispositioned within the bore 80 above the impact pin 78, and normallyurges the pin downwardly against the top of the stop block 77.

The spring force applied to the impact pin may be adjusted by means of ascrew 82, which threadedly engages the upper cross member 4 and has astud portion 83 extending downwardly into the bore 80, and around whichthe upper part of the spring 81 is located. Adjusting the screw member82 upwardly or downwardly will control the compressive force of thespring.

Preferably, the stop block 77 is so positioned that its upper face isspaced slightly upwardly a distance .r from the normal position of atooth 68 on the second ratchet wheel 67. By thus spacing the stop abovethe center line of the ratchet wheel, the impact forces of the pin 78are absorbed by the stop block rather than a ratchet tooth, Also, byspacing the stop above the center line, there are no external forcestending to rotate the drum and the ratchet wheels in the oppositedirection.

As the pawl assembly picks up a tooth on the first ratchet wheel, andstarts to rotate it in a counterclock wise direction, the second ratchetwheel 67 will pick up the edge of the impact pin 78, causing the pin toslide upwardly in the guide block 79. As the ratchet wheel completes itsindex, the impact pin will slip off of the tooth of the second ratchetwheel and will drop down on the stop block ready for the next cycle. Theimpact pin has been positioned in such a manner that the stop block onthe driving member will rise into engagement with the next ratchet toothbefore the impact pin is free to drop down to the stop block. Thus, bythis deceleration plunger assembly, I have provided additional orsupplemental means for preventing an unwanted rotation of the ratchetwheel assembly, which might not be taken care of otherwise when themember being indexed provides speed or other forces which will tend torotate the ratchet wheels at a greater speed than is pro vided by thenormal operation of the pawls.

From the foregoing, it will be apparent that there has been providedherein a novel stepping motor, preferably, although not necessarily,operated by an electropneumatic arrangement, wherein an arrangement ofdouble pawls operate to drive the motor at a high rate of speed.Furthermore, novel means have been provided in various forms of theinvention to positively lock the ratchet wheel at the end of eachindexing step so that it will be held against rotation in eitherdirection. It will be apparent, also, that certain features of theinvention may be utilized with only one pawl instead of two, if desired.

Changes may be made in the form, construction and arrangement of partsfrom those disclosed herein without in any way departing from the:spirit of the invention or sacrificing any of the attendant advantagesthereof, provided, however, that changes fall within the scope of theclaims appended hereto.

I claim:

1. A stepping motor for driving a rotary member intermittently,comprising,

a. a supporting frame,

b. a driving member mounted on said frame for reciprocating movement ina linear path,

means for reciprocating said driving member,

d. a ratchet wheel mounted on said rotary member,

e. two pawls mounted on and reciprocable with said driving member inopposed relation to each other and in the plane of said ratchet wheel,whereby reciprocation of said driving member will advance said ratchetwheel one step for each direction of movement of said driving member,and locking means associated with each of said pawls and cooperatingtherewith to restrain movement of said ratchet wheel in both directionswhen a pawl has completed its indexing movement.

2. A stepping motor, as defined in claim 1, wherein each of said lockingmeans is mounted on said frame.

3. A stepping motor, as defined in claim 1, combined with a secondratchet wheel rotatable with the first ratchet wheel on the same axisand having the teeth thereon disposed in a direction opposed to those onthe first ratchet wheel, and wherein each of said locking means ismounted on said driving member adjacent its associated pawl and ismovable into the path of a tooth on said second ratchet wheel when itsassociated pawl is advancing said first ratchet wheel.

4. A stepping motor, as defined in claim 3, combined with supplementalmeans cooperating with said second ratchet wheel and operable to preventmovement of said first ratchet wheel away from the driving pawl in theindexing direction thereof.

5. A stepping motor, as defined in claim 4, wherein said supplementalmeans comprises a yieldable member mounted in the path of movement ofthe teeth on said second ratchet wheel and adapted to be moved awaytherefrom by rotation of said second ratchet wheel when being indexed,and to return to its position in the path of the next succeeding tooththereon before the indexing step has been completed.

6. A stepping motor, as defined in claim 5, including a stop membermounted on said frame against which said yieldable member normallyrests.

7. A stepping motor, as defined in claim 6, wherein the surface of saidstop member against which said yieldable member normally rests is in aplane substantually parallel with and spaced from the plane of the faceof said next'succeeding tooth, whereby, when said yieldable memberreturns to its position in the path of said next succeeding tooth itwill come against said stop member instead of said tooth.

8. A stepping motor, as defined in claim 1, wherein said means forreciprocating said driving member includes pneumatically actuated pistonmeans operatively associated therewith, and control valve means operableto actuate said piston means.

9. A stepping motor, as defined in claim 8, including electrical meansfor operating said control valve means.

10. A stepping motor, as defined in claim 8, wherein said pneumaticallyactuated piston means includes a cylinder adjacent each end of saidframe, a piston reciprocable in each cylinder, and mean between eachsaid piston and the adjacent end of said driving member operable to movesaid driving member in a direction away from one of said cylinders whenair under pressure is admitted to said one cylinder.

11. A stepping motor, as defined in claim 10, wherein said last namedmeans includes a floating pin within a bore of each said piston havingone end thereof received within a recess in the adjacent end of saiddriving member.

12. A stepping motor, as defined in claim 10, wherein said control valvemeans is operable to direct air under pressure alternately to saidpiston means.

13. A stepping motor, as defined in claim 8, wherein said pneumaticallyactuated piston means includes a cylinder at one end of said drivingmember, a double acting piston therein, and a piston rod connected between said piston and one end of said driving member.

14. A stepping motor, as defined in claim 1, wherein said means forreciprocating said driving member includes crank means secured to oneend of said driving member.

15. A stepping motor, as defined in claim 1, including control meansoperable in response to movement of said driving member in onedirection, to cause movement of said driving member in the oppositedirection.

16. A stepping motor, as defined in claim 1, wherein said means forreciprocating said driving member includes pneumatically actuated pistonmeans operatively associated therewith, control valve means operable toactuate said piston means, and means operable in response to movement ofsaid driving member to actuate said control valve means and reverse thedirection of movement of said driving member.

17. A stepping motor, as defined in claim 1, wherein said means forreciprocating said driving member in cludes pneumatically actuatedpiston means operatively associated therewith, control valve meansoperable to actuate said piston means, electrical switch means operablein response to movement of said driving member to actuate said controlvalve means and reverse the direction of movement of said drivingmember.

18. A stepping motor for driving a rotary member intermittently,comprising a. a supporting frame,

b. a driving member mounted on said frame for reciprocating movement ina linear path,

c. means for reciprocating said driving member,

d. a first ratchet wheel mounted on said rotary member,

e. a pawl mounted on and reciprocable with said driving member in theplane of said first ratchet wheel, whereby reciprocation of said drivingmember in the operating direction of said pawl will advance said ratchetwheel one step,

f. a second ratchet wheel mounted on said rotary -member having theteeth thereon oppositely disposed withh respect to the teeth on saidfirst ratchet wheel, and

g. locking means movable into the path of a tooth on said second ratchetwheel during indexing thereof to prevent unwanted movement of saidrotary member in the driving direction of movement of said pawl.

19. A stepping motor, as defined in claim 18, wherein said locking meansis mounted on said driving member adjacent to said pawl.

20. A stepping motor, as defined in claim 18, wherein said means forreciprocating said driving member includes penumatically actuated pistonmeans operatively associated therewith, and control valve means operableto actuate said piston means.

21. A stepping motor, as defined in claim 20, including electrical meansfor operating said control valve means.

22. A stepping motor, as defined in claim 21, includ ing means operablein response to reciprocation of said driving member to actuate saidelectrical means.

23. A stepping motor, as defined in claim 18, combined with supplementalmeans cooperating with said second ratchet wheel operable to preventunwanted in the path of the next succeeding tooth thereon beforecompleted.

the indexing step has been I l =l

1. A stepping motor for driving a rotary member intermittently,comprising, a. a supporting frame, b. a driving member mounted on saidframe for reciprocating movement in a linear path, means forreciprocating said driving member, d. a ratchet wheel mounted on saidrotary member, e. two pawls mounted on and reciprocable with saiddriving member in opposed relation to each other and in the plane ofsaid ratchet wheel, whereby reciprocation of said driving member willadvance said ratchet wheel one step for each direction of movement ofsaid driving member, and f. locking means associated with each of saidpawls and cooperating therewith to restrain movement of said ratchetwheel in both directions when a pawl has completed its indexingmovement.
 2. A stepping motor, as defined in claim 1, wherein each ofsaid locking means is mounted on said frame.
 3. A stepping motor, asdefined in claim 1, combined with a second ratchet wheel rotatable withthe first ratchet wheel on the same axis and having the teeth thereondisposed in a direction opposed to those on the first ratchet wheel, andwherein each of said locking means is mounted on said driving memberadjacent its associated pawl and is movable into the path of a tooth onsaid second ratchet wheel when its associated pawl is advancing saidfirst ratchet wheel.
 4. A stepping motor, as defined in claim 3,combined with supplemental means cooperating with said second ratchetwheel and operable to prevent movement of said first ratchet wheel awayfrom the driving pawl in the indexing direction thereof.
 5. A steppingmotor, as defined in claim 4, wherein said supplemental means comprisesa yieldable member mounted in the path of movement of the teeth on saidsecond ratchet wheel and adapted to be moved away therefrom by rotationof said second ratchet wheel when being indexed, and to return to itsposition in the path of the next succeeding tooth thereon before theindexing step has been completed.
 6. A stepping motor, as defined inclaim 5, including a stop member mounted on said frame against whichsaid yieldable member normally rests.
 7. A stepping motor, as defined inclaim 6, wherein the surface of said stop member against which saidyieldable member normally rests is in a plane substantually parallelwith and spaced from the plane of the face of said next succeedingtooth, whereby, when said yieldable member returns to its position inthe path of said next succeeding tooth it will come against said stopmember instead of said tooth.
 8. A stepping motor, as defined in claim1, wherein said means for reciprocating said driving member includespneumatically actuated piston means operatively associated therewith,and control valve means operable to actuate said piston means.
 9. Astepping motor, as defined in claim 8, including electrical means foroperating said control valve means.
 10. A stepping motor, as defined inclaim 8, wherein said pneumatically actuated piston means includes acylinder adjacent each end of said frame, a piston reciprocable in eachcylinder, and mean between each said piston and the adjacent end of saiddriving member operable to move said driving member in a direction awayfrom one of said cylinders when air under pressure is admitted to saidone cylinder.
 11. A stepping motor, as defined in claim 10, wherein saidlast named means includes a floating pin within a bore of each saidpiston having one end thereof received within a recess in the adjacentend of said driving member.
 12. A stepping motor, as defined in claim10, wherein said control valve means is operable to direct air underpressure alternately to said piston means.
 13. A stepping motor, asdefined in claim 8, wherein said pneumatically actuated piston meansincludes a cylinder at one end of said driving member, a double actingpiston therein, and a piston rod connected between said piston and oneend of said driving member.
 14. A stepping motor, as defined in claim 1,wherein said means for reciprocating said driving member includes crankmeans secured to one end of said driving member.
 15. A stepping motor,as defined in claim 1, including control means operable in response tomovement of said driviNg member in one direction, to cause movement ofsaid driving member in the opposite direction.
 16. A stepping motor, asdefined in claim 1, wherein said means for reciprocating said drivingmember includes pneumatically actuated piston means operativelyassociated therewith, control valve means operable to actuate saidpiston means, and means operable in response to movement of said drivingmember to actuate said control valve means and reverse the direction ofmovement of said driving member.
 17. A stepping motor, as defined inclaim 1, wherein said means for reciprocating said driving memberincludes pneumatically actuated piston means operatively associatedtherewith, control valve means operable to actuate said piston means,electrical switch means operable in response to movement of said drivingmember to actuate said control valve means and reverse the direction ofmovement of said driving member.
 18. A stepping motor for driving arotary member intermittently, comprising a. a supporting frame, b. adriving member mounted on said frame for reciprocating movement in alinear path, c. means for reciprocating said driving member, d. a firstratchet wheel mounted on said rotary member, e. a pawl mounted on andreciprocable with said driving member in the plane of said first ratchetwheel, whereby reciprocation of said driving member in the operatingdirection of said pawl will advance said ratchet wheel one step, f. asecond ratchet wheel mounted on said rotary member having the teeththereon oppositely disposed withh respect to the teeth on said firstratchet wheel, and g. locking means movable into the path of a tooth onsaid second ratchet wheel during indexing thereof to prevent unwantedmovement of said rotary member in the driving direction of movement ofsaid pawl.
 19. A stepping motor, as defined in claim 18, wherein saidlocking means is mounted on said driving member adjacent to said pawl.20. A stepping motor, as defined in claim 18, wherein said means forreciprocating said driving member includes penumatically actuated pistonmeans operatively associated therewith, and control valve means operableto actuate said piston means.
 21. A stepping motor, as defined in claim20, including electrical means for operating said control valve means.22. A stepping motor, as defined in claim 21, including means operablein response to reciprocation of said driving member to actuate saidelectrical means.
 23. A stepping motor, as defined in claim 18, combinedwith supplemental means cooperating with said second ratchet wheeloperable to prevent unwanted movement of said first ratchet wheel awayfrom the driving pawl in the indexing direction thereof.
 24. A steppingmotor, as defined in claim 23, wherein said supplemental means comprisesa yieldable member mounted in the path of movement of the teeth on saidsecond ratchet wheel and adapted to be cammed by said second ratchetwheel in a direction away therefrom when being indexed, and to return toits position in the path of the next succeeding tooth thereon before theindexing step has been completed.